Method of Treating A Degenerate Spinal Segment

ABSTRACT

A method of treating a degenerate spinal segment comprises obtaining a first spinal implant configured to apply a first torque to a degenerate spinal segment having an abnormal curvature and a second spinal implant configured to apply a second torque to said degenerate spinal segment. Each of said spinal implants includes; a plurality of contiguous segments in which said contiguous segments form an angle at a location in which two adjacent contiguous segments of the plurality of contiguous segments intersect; and at least one mounting connection configured to connect said spinal implant to a mounting mechanism, said mounting mechanism being configured to attach said spinal implant to said degenerate spinal segment. Said first spinal implant and said second spinal implant are implanted to said degenerate spinal segment so that said first torque and said second torque act to reduce said abnormal curvature.

PRIORITY CLAIM

This application claims the benefit of and priority from U.S.Provisional Patent Application No. 61/208,018 filed on Feb. 19, 2009,and U.S. Provisional Patent Application No. 61/210,740 filed on Mar. 19,2009, which are each incorporated herein in their entirety for allpurposes by this reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Research leading to this application was sponsored, in part, throughNational Science Foundation Award No. CMMI-0800606, “Lamina EmergentMechanisms.”

FIELD

Embodiments of the present invention relate generally to mechanicalspinal implants and, more particularly, to dynamic spinal implants thatrelieve symptoms of degenerative spinal diseases, that restore healthymotion to an unhealthy spine, and that promote the healing of spinaltissues.

BACKGROUND

The human spine functions through a complex interaction of several partsof the anatomy. FIGS. 1 and 2 (the cross-section A-A of FIG. 1)illustrate a segment of the spine 4, with vertebra 5. The vertebra 5include the vertebral body 6, the spinous process 8, transverse process10, pedicle 12, and laminae 14. A functional spine, comprising severalvertebra 5, typically subcategorized as being part of the cervical,thoracic, lumbar, sacral, and coccygeal regions as known, providessupport to the head, neck, trunk, and transfer weight to lower limbs,protects the spinal cord 20, from which peripheral nerves 32 extend, andmaintain the body in an upright position while sitting or standing.

Also illustrated in FIGS. 1 and 2, the spinal segment 4 includesintervertebral discs 20 that separate adjacent vertebra 5. Theintervertebral discs 20 provide motion, load bearing and cushioningbetween adjacent vertebrae 5. Intervertebral discs 20 are the largestavascular structure in the body, relying on diffusion for its nutrition.The diffusion of nutrients is aided by the compression cycles that theintervertebral discs 20 undergo during the course of normal movement,which drives out waste products and cycles fluids. Lying down andresting reduces the load on the intervertebral discs 20 allowingnutrients to diffuse into the intervertebral discs 20.

Also illustrated in FIGS. 1 and 2, the spinal segment includes spinalfacet joints 16. Spinal facet joints 16 join the adjacent vertebrae 6.The spinal facet joints 16 are synovial joints that function much likethose of the fingers. Together with the intervertebral disc 20, thespinal facet joints 16 function to provide proper motion and stabilityto a spinal segment 4. Thus, each spinal segment 4 includes threejoints: the intervertebral disc 20 in the anterior aspect of the spinalsegment 4 and the two spinal facet joints 16 in the posterior aspect ofthe spinal segment 4.

For the spinal segment 4 to be healthy, each of the intervertebral disc20 and the spinal facet joints 16 must be healthy. To remain healthythese joints require motion. The intervertebral disc 20 and the spinalfacet joints 16 function together to provide both quality and quantityof motion. The quality of the motion is a exhibited by the non-linearenergy storage (force-deflection, torque-rotation) behavior of thespinal segment 4. The quantity of motion is the range of segmentalrotation and translation.

Back pain due to diseased, damaged, and/or degraded intervertebral discs20 and/or spinal facet joints 16 is a significant health problem in theUnited States and globally. A non-exhaustive and non-limitingillustration of examples of diseased and/or damaged intervertebral discsare shown in FIG. 3. While a healthy intervertebral disc 20 isillustrated at the top of the spine segment 18, diseased and/or damageddiscs are also illustrated. The diseased and/or damaged discs include adegenerated disc 22, a bulging disc 24, a herniated disc 25, a thinningdisc 26, discs indicating symptoms of degeneration with osteophyteformation 28, as well as hypertrophic spinal facets 29.

A degenerating spinal segment 18 is believed to be the product ofadverse changes to its biochemistry and biomechanics. These adversechanges create a degenerative cascade affecting the quality and/orquantity of motion and may ultimately lead to pain. For example, as thehealth of a spinal segment 18 degenerates and/or changes, the spacethrough which the spinal cord 30 and peripheral nerves 32 (FIGS. 1 and2) pass can become constricted and thereby impinge a nerve, causingpain. For example, the spinal cord 30 or peripheral nerves 32 may becontacted by a bulging disc 24 or herniated disc 25 or hypertrophicspinal facet 29 as illustrated in FIG. 3. As another example, a changein the spinal segment 18, such as by a thinning disc 26 may alter theway in which the disc functions, such that the disc and spinal facetsmay not provide the stability or motion required to reduce muscle,ligament, and tendon strain. In other words, the muscular system isrequired to compensate for the structural deficiency and/or instabilityof the diseased spinal segment 18, resulting in muscle fatigue, tissuestrain, and hypertrophy of the spinal facets, further causing back pain.The pain this causes often leads patients to limit the pain-causingmotion; but this limited motion, while offering temporary relief, mayresult in longer-term harm. because the lack of motion limits theability of the disc to expel waste and obtain nutrients as discussedabove.

Of course, other diseases of the disc and other back related problemsand/or maladies afflict many people. For example, as the discdegenerates the spinal facet joints undergo a change in motion and inloading. This causes the spinal facet joints to begin to degenerate.Spinal facet joint arthritis is an additional source of pain. Also,scoliosis, or a lateral curvature of the spine, is illustrated in FIG.4. A patient's body 40 is illustrated in outline. Also illustrated isthe lateral curvature of a scoliotic spine 42 that is afflicted withscoliosis. The scoliotic center line 44 of the scoliotic spine 42 isillustrated, as compared to a healthy centerline or axis 46 of a healthyspinal column or functional spine unit. Conditions such as kyphosis, anexaggerated outward-posterior curvature of the thoracic region of thespine resulting in a rounded upper back, lordosis, an exaggeratedforward curvature of the lumbar and cervical regions of the spine, andother conditions also afflict some patients.

In many instances of degenerative disc disease, fusion of the vertebraeis the standard of care for surgical treatment, illustrated in FIG. 5.In the U.S. alone, approximately 349,000 spinal fusions are performedeach year at an estimated cost of $20.2 billion. The number of lowerback, or lumbar, fusions performed in the U.S. is expected to grow toapproximately 5 million annually by the year 2030 as the populationages, an increase of 2,200%.

Spinal fusion aims to limit the movement of the vertebra that areunstable or causing a patient pain and/or other symptoms. Spinal fusiontypically involves the removal of a diseased disc 50, illustrated inoutline in FIG. 5. The removed disc 50 is replaced by one or more fusioncages 52, which are filled or surrounded by autograft bone thattypically is harvested by excising one or more spinal facet joints 57.Vertebral bodies 51 adjacent the removed disc 50 are stabilized with oneor more posterior supports 58 that are fixedly connected to thevertebral bodies 51 with the use of pedicle screws 54 that arescrewed—such as by use of a bolt-style head 56 to turn the pedicle screw54—into a hole drilled into the pedicle 12 of the vertebral bodies 51.

Fusion, however, often fails to provide adequate or sufficient long-termrelief in about one-half of the treatments, resulting in low patientsatisfaction. Further, fusion, by definition, restricts the overallmotion of the treated functional spine unit, imposing increased stressesand range of motion on those portions of the spinal segment adjacent tothe fused vertebral bodies 51. Fusion of a spinal segment has beenindicated as a potential cause of degeneration to segments adjacent tothe fusion. The adjacent spinal facet joints 57 and adjacent discs 59often have to bear a greater load as a result of the fusion than wouldtypically be the case, leading to possible overloading and, in turn,degeneration. Thus, surgical fusion often provides short-term relief,but possibly greater long-term spinal degradation than would otherwisehave occurred.

Thus, a challenge to alleviating the back pain associated with variousailments is to find a remedy that, ideally, does not involve removingthe diseased disc or damaging the spinal facet joints, and that providessufficient stability to the diseased segment to alleviate pain and/orother symptoms, while still providing sufficient freedom of movement toallow the disc and spinal facet joints to return to health.

A further challenge is simply the complex, multi-dimensional nature ofmovement associated with a functional spine unit. Illustrated in FIG. 6are the varying, orthogonal axes around which a functional spine unitmoves. For example, a vertebra 5 is illustrated with an X-axis 60,around which a forward bending motion, or flexion, 61 in the anteriordirection occurs. Flexion 61 is the motion that occurs when a personbends forward, for example. A rearward bending motion, or extension, 62is also illustrated. The Y-axis 63 is the axis around which lateralextension, or bending, 64, left and right, occurs. The Z-axis 65 is theaxis around which axial rotation 66, left and right, occurs. Spinalfusion, as discussed above, limits or prevents flexion 61-extension 62,but also limits or prevents motion in lateral extension, or bending, 64and axial rotation 66. Thus, an improved alternative remedy to fusionpreferably allows for movement with improved stability around each ofthe three axes, 60, 63, and 65.

Another difficulty associated with the complex motion of the spine isthat the center-of-rotation for movement around each of the X-axis 60,Y-axis 63, and Z-axis 65 differs for each axis. This is illustrated inFIG. 7, in which the center-of-rotation for the flexion 61-extension 62motion around the X-axis 60 is located at flexion-extensioncenter-of-rotation 70. The center-of-rotation for the lateral extension,or bending, 64 motion around the Y-axis 63 is located at lateralextension, or bending, center-of-rotation 73. The center-of-rotation forthe axial rotation 66 around the Z-axis 65 is located at axial rotationcenter-of-rotation 75. For more complex motion patterns (e.g., combinedflexion, lateral extension/bending, etc.) a two-dimensionalrepresentation of the center-of-rotation is inadequate, but thethree-dimensional equivalent called the helical axis of motion, orinstantaneous screw axis can be employed. Spinal remedies which forcerotation of a spinal segment around any axis other than the naturalhelical axis impose additional stresses on the tissue structures at boththe diseased spinal segments and the adjacent spinal segments.Compounding the issue for the centers-of-rotation is that they actuallychange location during the movement, i.e., the location of thecenters-of-rotation are instantaneous. Thus, a preferable remedy tospinal problems would account for the different instantaneouscenters-of-rotation throughout the range of motion. Stated differently,a preferable remedy to spinal problems would allow the diseased spinalsegment and adjacent spinal segments to under motion approximate that ofthe natural helical axis through the range of motions.

Many previous efforts have been made to solve at least some of theproblems associated with spinal fusion, but with varying degrees ofsuccess. For example, U.S. Pat. No. 7,632,292 (the '292 patent) toSengupta and Mulholland, discloses an arched-shaped spring mechanismthat is attached to adjacent vertebrae via pedicle screws. This devicerelies on the extension and compression of the spring to accommodateflexion 61 and extension 62 about the X-axis 60 illustrated in FIG. 6.The device disclosed in the '292 patent addresses only flexion-extensionand neither lateral extension/bending nor axial rotation, which wouldboth still be improperly supported. Further, the '292 patent does notaccount for the instantaneous centers-of-rotation; in other words, thecenters-of-rotation will be misplaced for motions other than flexion. Inaddition, it may be anticipated that the device is either too stiff toprovide proper motion or that the extension-compression cycles may leadto fatigue failure of the device.

Another example is U.S. Pat. No. 6,966,910 (the '910 patent) and itsassociated family of applications to Ritland. As with the '292 patent,the '910 patent relies on the extension-compression cycle of a springmechanism—specifically the reverse curves within the mechanism—toaccommodate flexion 61 and extension 62 about the X-axis 60 illustratedin FIG. 6. Lateral extension/bending and axial rotation are notaddressed.

Thus, there exists a need for a spinal implant that protects the spinalcord and the peripheral nerves from damage.

Further, there exists a need for a spinal implant that reduces thestress on a diseased and/or damaged disc without overloading theadjacent discs and vertebrae that could initiate progressivedegeneration or diseases in the adjacent discs and vertebrae.

Another need exists for a spinal implant that minimizes or avoids wear.Previous spinal implants that have parts that move against each othermay cause wear particles or debris—i.e., small pieces of the implant—tocome free, potentially loosening the implant and/or decreasing thestability of the implant, and/or potentially causing adjacent bone ortissue to degrade because of contamination. Further, wear particles maychange the chemical structure and/or chemical stability of biocompatibledevices such that the resultant chemical structure and/or chemicalstability becomes non-biocompatible or causes the implant to degrade atan accelerated rate.

A need also exists for a spinal implant that provides for properforce-deflection behavior of the spinal implant (kinetics)—as notedabove in the discussion of FIG. 6—preferably to approximate those of anormal, functional spine unit to relieve the load and strain on theintervertebral discs, to protect the spinal facet joints, to reduce therisk of damage to segments of the spine adjacent to the diseasedsegment, to reduce muscle fatigue and reduce and/or eliminate subsequentpain.

A need also exists for a spinal implant that exhibits kinematics—such asthe limits of the ranges-of-motion and the centers-of-rotation notedabove in the discussion of FIG. 7—that, preferably, are maintained nearthose of a functional spine unit to maintain an effective range ofmotion for the intervertebral discs, spinal facet joints, muscles,ligaments, and the tendons around the spine and to reduce the amount ofneural element strain, e.g., the strain on the spinal cord and/or otherparts of the nervous system.

A need still exists for a spinal implant that relieves a portion of theload that would otherwise be borne by the diseased disc. In addition, acompliant spinal implant preferably distracts (or extends) thespace—including the space anteriorly and/or posteriorly—between thevertebrae adjacent to the diseased discs.

In addition, a need exists for a spinal implant that preferably restoresa torque-rotation signature near that of a healthy, functional spineunit.

Spinal implants including one or more of the recited features andbenefits could improve the opportunity for the diseased spinal segmentand/or intervertebral discs and/or spinal facet joints to heal.

SUMMARY

Various features and embodiments of the invention disclosed herein havebeen the subject of substantial ongoing experimentation and have shown asignificant improvement over the prior art. Among other improvements,the embodiments of the invention provide robust and durable compliantspinal implants that have a smaller profile and accommodate motion inthree axes as compared to a single axis of motion of the prior art. Itis believed that the embodiments, collectively and/or individually,represent an unexpected advance in the field and will enable physiciansto provide spinal implants that can be selected and individuallyadjusted pre-operatively, intra-operatively (i.e., during theoperation), and post-operatively to restore the normal or near normalfunction of a damaged or diseased spinal segment.

Embodiments of the compliant dynamic spinal implant include a geometrythat, once implanted, is configured to allow flexion-extension, and/orlateral extension/bending, and/or axial rotation with an instantaneousor near-instantaneous centers-of-rotation for the diseased and/ordamaged disc and adjacent vertebrae that are similar to that of ahealthy spinal segment. Thus, the implant restores, to a degree, closeto normal movement of the diseased and/or damaged discs and adjacentvertebrae, which, in turn, promotes healing of the diseased and/ordamaged disc.

Other embodiments of the spinal implant provide protection to the spine,discs, spinal cord, and peripheral nerves by reducing the risk ofharmful, damaging, and/or painful movements while still providing asufficient range of motion to promote healing and while reducing therisk of damage and/or disease to adjacent discs and vertebrae.Embodiments of the spinal implant do so by reducing the stresses on adiseased and/or damaged spinal segment without overloading the adjacentspinal segments, including the adjacent intervertebral discs, spinalfacet joints, and vertebrae, that could initiate progressivedegeneration or diseases in the adjacent spinal segments. For example,embodiments of a spinal implant preferably relieve a portion of thecompressive load that would otherwise be borne by the diseased disc and,preferably, distracts (or increases) the space between the vertebraeadjacent to the diseased discs, which improves the opportunity for thediseased disc to heal.

Embodiments of the spinal implant preferably provide forforce-deflection behaviors near those of a normal, functional spineunit—such as the healthy discs and/or spinal facet joints near thedamaged and/or diseased spinal segments of a patient—to reduce musclefatigue and subsequent pain. Additionally, embodiments of the spinalimplant preferably provide proper motion—such as thecenters-of-rotation, whether instantaneous or otherwise, limits of theranges-of-motion, and the types of motion—that are maintained near thoseof a functional spine unit to maintain an effective range of motion forthe muscles and the tendons around the spine and to reduce the amount ofspinal cord strain. For instance, embodiments of the compliant spinalimplant preferably restore a torque-rotation signature near that of ahealthy, functional spine unit.

Embodiments of the present invention exhibit reduced or limited wearcompared to prior art devices. Such reduced wear is provided,preferably, by having few to no parts within the implant itself thatmove or wear against other parts of the spinal implant or against thevertebrae and/or other skeletal tissue that might cause the implant towear. Thus, embodiments of the spinal implant produce few to no wearparticles when compared to prior devices.

Further embodiments include spinal implants that have a geometryengineered and configured to provide one or more of the above benefits.Embodiments of the spinal implant include a first attachment on a firstlength and a second attachment on a second length. Each attachment isconfigured for connecting and attaching to a device (typically, althoughnot necessarily, pedicle screws and other similar devices) fortemporarily or permanently fixing the spinal implant to one or morevertebrae. The first length and the second length are joined by a thirdsection having a geometry engineered to provide one or more of the abovebenefits. The spinal implant preferably relies upon the geometry and thematerial from which the implant is manufactured to provide torque tooppose the flexion-extension of the spine, rather thancompression-extension as in prior art devices. In addition, the spinalimplant preferably relies upon the geometry and the material from whichthe implant is manufactured to provide compression and extension tooppose the lateral extension/bending of the spine.

Embodiments of the spinal implant are preferably made of biocompatiblematerials, including, but not limited to, biocompatible polymers andplastics, bioabsorbable materials, stainless steel, titanium, nitinol,shape-memory materials and/or alloys, and other similar materials.Additionally, embodiments of the spinal implant can be manufactured withmaterials that provide for pre-operative, operative, and post-operativeadjustment of the implant and the manner in which it responds to a giveninput such as stress and/or torque, and, in the instance ofpost-operative adjustment, preferably adjustment through minimallyinvasive techniques and, more preferably, through non-invasivetechniques. Embodiments of methods of adjusting the spinal implant arealso disclosed.

Embodiments of methods of implanting the spinal implant are alsodisclosed.

Methods of using the above described system to detect leaks are alsodisclosed.

As used herein, “at least one,” “one or more,” and “and/or” areopen-ended expressions that are both conjunctive and disjunctive inoperation. For example, each of the expressions “at least one of A, Band C,” “at least one of A, B, or C,” “one or more of A, B, and C,” “oneor more of A, B, or C” and “A, B, and/or C” means A alone, B alone, Calone, A and B together, A and C together, B and C together, or A, B andC together.

Various embodiments of the present inventions are set forth in theattached figures and in the Detailed Description as provided herein andas embodied by the claims. It should be understood, however, that thisSummary does not contain all of the aspects and embodiments of the oneor more present inventions, is not meant to be limiting or restrictivein any manner, and that the invention(s) as disclosed herein is/are andwill be understood by those of ordinary skill in the art to encompassobvious improvements and modifications thereto.

Additional advantages of the present invention will become readilyapparent from the following discussion, particularly when taken togetherwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

To further clarify the above and other advantages and features of theone or more present inventions, reference to specific embodimentsthereof are illustrated in the appended drawings. The drawings depictonly exemplary embodiments and are therefore not to be consideredlimiting. One or more embodiments will be described and explained withadditional specificity and detail through the use of the accompanyingdrawings in which:

FIG. 1 is a segment of a functional spine unit;

FIG. 2 is a cross-section of the segment of the functional spine unitillustrated in FIG. 1, taken along section A-A of FIG. 1;

FIG. 3 is a segment of a spine illustrating various pathologies ofintervertebral discs;

FIG. 4 is a scoliotic spine;

FIG. 5 is a prior art discectomy and spinal fusion;

FIG. 6 illustrates the three axes of motion around which functionalspine unit moves;

FIG. 7 illustrates the centers-of-motion of a functional spine unit;

FIG. 8 illustrates an embodiment of an unimplanted compliant dynamicspinal implant, shown from the rear/posterior view, i.e., as it wouldappear from the rear of a person when implanted;

FIG. 9 is a lateral/side view of the spinal implant shown in FIG. 8;

FIG. 10 shows embodiments of the spinal implant as they would appearimplanted in a pair of lumbar vertebrae as viewed from the rear;

FIG. 11 is a lateral/side view of one of the spinal implants of FIG. 10;

FIG. 12 is a posterior view of the spinal implant of FIG. 8 undergoing atorsional load;

FIG. 13 is a lateral view of the spinal implant of FIG. 9 undergoing atorsional load;

FIG. 14 is a posterior view of the spinal implant of FIG. 8 undergoing acompressive load and a torsional load;

FIG. 15 is a lateral view of the spinal implant of FIG. 9 undergoing acompressive load and a torsional load;

FIG. 16 is a graph of the rotation that occurs for a given torque for anexemplary healthy spine and an exemplary degenerative spine undergoingflexion and extension;

FIG. 17 is a graph of the moment difference between the response of thedegenerative spine and the healthy spine graphed in FIG. 16 and a linearcurve fit of the moment difference; and,

FIG. 18 is a graph of the healthy spine of FIG. 16 and the resultantrotation that occurs for a given torque of the degenerative spine (shownin FIG. 16) that has had an embodiment of the spinal implant that hasbeen adjusted to exhibit a torque response that is the negative slope ofthe linear curve fit shown in FIG. 17.

The drawings are not necessarily to scale.

DETAILED DESCRIPTION

As noted above, the kinetics and kinematics of the spine are quitecomplex, involving three separate axes around which motion occurs andthree separate centers-of-rotation for the different motions. Applicantshave recognized that previous spinal implants often address just oneform of motion, typically flexion and extension, often through the useof springs of some type that flex and compress. Efforts to address morethan one mode of rotation or motion typically tend to be complex, large,and often do not address each individual motion as effectively asdevices dedicated to a single motion.

Through significant experimentation and engineering work, Applicantshave discovered geometries that rely, in part, on the concept oftorsion, rather than primarily compression and extension of springs, toprovide a seemingly simple, yet decidedly complex, geometry thataccommodates motion and stiffness around the three axis and accommodatesthe separate centers-of-rotation for each motion (flexion-extension,lateral extension or bending, and axial rotation). A compliant mechanismgains its motion from the deflection of flexible, resilient members.Such devices move without the aid of traditional sliding joints andbearings, thus increasing precision and eliminating friction and wear.They also integrate spring and hinge functions, allowing for the designof desired force-deflection behavior.

An embodiment of a compliant dynamic spinal implant 100 is illustratedin FIGS. 8 and 9, which is an embodiment of a geometry thataccomplishes, in part, the objectives provided above and in thebackground section. A posterior view of the spinal implant 100 ispresented in FIG. 8—reference being made to the direction the spinalimplant would be viewed from when implanted in a patient. In otherwords, the spinal implant 100 in FIG. 8 appears as it would as viewed itfrom the patient's back. A lateral, or side, view, of the implant ispresented in FIG. 9. It will be understood that while these referencesto view are presented for clarity, it should be understood the spinalimplants 100 shown in FIGS. 8 and 9 appear in their unstressed,pre-implant condition, as will be explained in further detail below. Inthis particular embodiment, the spinal implant 100 comprises a pluralityof contiguous segments. In one embodiment, these contiguous segmentsinclude a first segment 101, having a first length 107, a first width111, and a first height or thickness 118; a second segment 102 having asecond length 108, a second width 112, and a second height or thickness119; a third segment 103 having a third length 109, a third width, and athird height or thickness; a fourth segment 104 having a fourth length,a fourth width 113, and a fourth height or thickness. The spinal implant100 also includes a fifth segment 105 having a fifth length 110, a fifthwidth 114, and a fifth height or thickness 120. Of course, one havingskill in the art would understand that other geometries andconfigurations exist—including greater or fewer segments—thataccomplish, in part, the recited objectives.

In this particular embodiment, the third width is the same width as thefourth width 113. Likewise, the fourth length is the same length as thethird length 109. Furthermore, the heights of each segment discussed,including, the third and fourth heights, are the same as the firstheight 118, second height 119, and fifth height 120, respectively. Ofcourse, the specific dimensions—including those not individuallydiscussed—may be the same or they may differ from each other as onehaving skill in the art would understand.

As illustrated, the plurality of segments form angles at the location inwhich adjacent segments intersect. In other words, a plurality of anglesexist, one angle for each intersection between two adjacent segments.For example, the first segment 101 is joined to the third segment 103,creating a first angle 115 between the first segment 101 and the thirdsegment 103. The third segment 103 is joined to the fifth segmentcreating a second angle 117. The fifth segment 105 is, in turn, joinedto the fourth segment 104, creating a third angle that, in thisinstance, is the same angle as the second angle 117. The fourth segment104, in turn, is joined to the second segment 102, creating a fourthangle 116.

When reference is made to that the individual segments being “joined,”it is understood that the segments may be temporarily joined, through aremovable connection, such as bolts, screws, biocompatible adhesives,and the like. Alternatively, one or more of the segments may be joinedpermanently, such as through the use of biocompatible epoxies, polymers,and other known methods of joining the segments. In yet anotherembodiment, the individual segments may be formed as a single, unitarypiece, such as by laminating, molding, pressing, stamping, milling, andother known methods.

In the embodiment illustrated, each of the angles 115, 116, and 117 areeach right angles, thus forming a “U” configuration or shape of thecontiguous segments, with each of the segments lying within proximatelythe same plane before implantation, although the measurement of eachangle may differ from the others and fall within a variety of ranges.For example, the measurement of one or more of the angles may range fromabout 80° to about 100°; from about 70° to about 110°; and from about45° to about 135°; and so forth.

As noted, embodiments of the spinal implant 100 use, in part, torsion toapply a force or load to the vertebrae of a patient. Typically, althoughnot necessarily, the spinal implant 100 has an initial curvature to thedevice, as indicated in FIG. 9 by torsion angle 122 with a radius ofcurvature 121. FIG. 9, in the pre-implanted condition, includes thistorsion angle 122, thus, as will be discussed below when explaining theprocedure to implant the device, the spinal implant will provide a knownor selected torque when it is straightened for implantation. Of course,the magnitude of this torque is a function of the radius of curvature121, the material from which the spinal implant 100, is manufactured,and the specific geometry of each of the individual segments.

The spinal implant 100 optionally includes at least one mountingconnection for connecting the spinal implant 100 to a mountingmechanism. For example, an embodiment of a mounting connection includesthrough holes 106 (FIG. 8), through which a mounting mechanism,typically, although not necessarily, pedicle screws, are positioned tohold the spinal implant in position in the patient—i.e., the mountingmechanism attaches the spinal implant 100 to at least a portion of aspinal segment, such as a vertebra, a pedicle, or other bony structureof a patient as will be discussed below. Of course, pedicle screws aremerely one example of a mounting mechanism for attaching the spinalimplant 100 to a patient's vertebrae. Other mounting mechanisms, such asthe use of pins, biocompatible adhesives, straps, and the like, fallwithin the scope of this disclosure.

The spinal implant 100 can be formed of biocompatible plastics,polymers, metals, metal alloys, laminates, shape-memory materials, andother similar materials, either wholly as one material or as acombination of materials—i.e., different segments may be manufacturedfrom different materials. Optionally, embodiments of the spinal implantcan be made from bioabsorbable materials that a patient's body willnaturally breakdown over time, thus potentially avoiding the need for asecond surgery to remove the spinal implant 100, should such an optionprove necessary and/or desirable.

An embodiment of the spinal implant 100 can optionally be made withnitinol, a metal alloy of nickel and titanium, that provides the abilityof shape-memory. A spinal implant 100 made from such materials would bemanufactured into a first shape or geometry or configuration (e.g., thelength of the first and second segments 101 and 102, the radius ofcurvature 121, etc.) having a known and desired first torque response.The spinal implant 100 would then be manipulated into a second shape orgeometry having a known and desired second torque response. The spinalimplant 100, in the second shape or geometry or configuration, thenwould be implanted in the patient. After implantation, a physician canapply an activating agent, such as heat, current, or other parameter, tocause the spinal implant 100 to revert back to its original, first shapeor geometry, allowing the material to consequently revert to its firsttorque response. Thus, a measure of adjustability in the torque responseof the spinal implant 100—even post-surgery—can be manufactured into thespinal implant 100. For example, in the case of nitinol, applying aparameter such as heat to the spinal implant and, in so doing, raisingthe spinal implant to a temperature above the transition temperature ofthe nitinol causes the spinal implant to revert to its first shape orgeometry. In so doing, the stiffness of the spinal implant could bealtered by, for example, making the spinal implant significantly stifferso that it approximates more closely the stiffness provided by a spinalfusion procedure.

Another embodiment of the spinal implant 100 can be made frombioabsorbable materials, as mentioned. The patient's body would slowlyabsorb the spinal implant 100 and, in the process of so doing, thecompressive load or force and torque provided or born by the spinalimplant 100 would slowly be transferred to the intervertebral discsand/or vertebrae of the patient as the patient's spine healed and/orimproved in health and strength. Thus, a bioabsorbable devicecontemplates and allows for a patient to regain his or her spinalhealth, an adjustment and transfer of force and torque from the spinalimplant to the patient's body, and the eventual removal of the spinalimplant through absorption rather than surgery.

An advantage of embodiments of the spinal implants disclosed—providedthat they are manufactured as single, unitary piece—is that they do nothave any joints or surfaces that might rub or wear against each otherbecause the embodiments rely on deflection of the segment(s) to providea force and/or torque. The relative lack of rubbing or movement againstother elements as compared to prior art devices minimizes or preventsthe formation of wear particles that might otherwise be generated. Thisis the case for those prior art devices that have biocompatible surfacesthat might wear off to expose non-biocompatible surfaces or, in someinstances, the wear causes the biocompatible surface to becomenon-biocompatible, leading to additional wearing of the prior artdevices at an accelerated rate.

For context, FIGS. 10 and 11 illustrate embodiments of the spinalimplant 200 as they might appear implanted on a lumbar portion of thespine of a patient. The spinal implants 200 are fixed to the vertebrae204 adjacent to a diseased disc 206. In this embodiment, pedicle screws202 are used to fix the spinal implants 200 to the vertebrae 204. (Themethod of surgical implantation will be discussed in more detail below.)Once implanted, the spinal implants 200 optionally provide an extensionforce 210, if they are prestressed, as will be discussed below, to helpdistract the vertebrae 204 from the diseased disc 206. Alternatively,the spinal implants 200 resist a compressive force 214 from the normalaction of gravity upon the person, thus supporting a portion of the loadthat would otherwise have been born by the diseased disc 206. Inaddition, the spinal implants provide a torque 212 (about an axisperpendicular to the page of FIG. 10) that distracts the diseased disc206 and, preferably, distracts an anterior portion 207 of the diseaseddisc 206. The torque 212 applied by the spinal implants 200 can beselected and adjusted to compensate at least partially and, preferably,almost fully, for the diseased disc 206, as will be explained furtherbelow.

Turning to FIGS. 12 and 13, these figures illustrate the spinal implants100 from FIGS. 8 and 9 as they might appear during surgicalimplantation. As noted in the discussion of FIG. 9 above, the spinalimplant 100 optionally is manufactured (or shaped, in the case ofshape-memory materials like nitinol) to have a first geometry, which mayinclude a first radius of curvature 121, the radius of curvature isabout an axis orthogonal to the axis of the spinal column (e.g., axis 44in FIG. 4). To implant the spinal implant 100, a surgeon could use apositioning tool that provides a torque 130 that causes the radius ofcurvature 121 to increase, potential to infinity, in the illustratedinstance. In such a position, the surgeon can fix the spinal implants100 to the patient's vertebrae (vertebrae 204 in FIGS. 10 and 11) withpedicle screws or other methods. Once the positioning tool is releasedand, consequently, torque 130 removed, the spinal implant 100 tends toreturn to its original, unstressed state and, in so doing, applies atorque 212 to the vertebrae 204 as illustrated in FIGS. 10 and 11.

FIGS. 14 and 15 illustrate the spinal implant 100 under a compressiveforce 142. This load could be caused by the normal action of gravitywhen implanted in a patient as the spinal implant 100 bears some of thecompressive load. Alternatively or in addition to the load of gravity,such a force may occur as a result of lateral extension—i.e., thepatient is leaning toward that side as a result of rotation 64 aroundthe Y-axis 63 illustrated in FIG. 6. As FIG. 14 indicates, the thirdsegment 103 and the fourth segment 104 deflect, causing a change in thefirst, second and fourth angles, 115, 117, and 116, respectively. Thedeflection of the segments 103 and 104 creates a torque that balancesthe compressive force 142.

In addition, a torque 140 can be applied to the spinal implant 100, asituation that might occur when the patient is leaning forward, causingflexion, i.e. a rotation around the X-axis 60 in the forward direction(flexion 61) in the spinal region in which the spinal implant 100 hasbeen fixed. Such a movement would cause compression of the anteriorregion 207 of a diseased disc 206 as illustrated in FIG. 11. The spinalimplant 100, by bending, applies a torque that would counteract, atleast in part, the torque 142 caused by flexion. As one having skill inthe art would understand, embodiments of the spinal implants 100 havinga selected geometry such as that illustrated, would provide similartorque to balance and/or offset other forces incurred throughflexion-extension, lateral extension/bending, and axial rotation.

A benefit of embodiments of the spinal implant are that it can beindividually adjusted to a specific patient and that patient'spathologies, rather than relying on prior art devices that weremanufactured for a predetermined subset of the population. Thedisadvantages of the latter approach are that it is rare that anindividual patient's pathologies, by coincidence, are an exact match fora device. Thus, the patient must compromise, to a greater or lesserextent, on the performance and the relief that may be obtained throughthe use of some prior art devices.

Referring to FIGS. 16-18, a process for selecting and adjusting a spinalimplant to a patient's pathology will be discussed. FIG. 16 is a graphof the torque-rotation response of a healthy and a diseased ordegenerative disc undergoing flexion and extension, i.e., rotation inflexion 61 and extension 62 around the X-axis 60 as illustrated in FIG.6 and corresponding to bending or leaning over and bending or leaningbackwards. The X-axis 300 of the graph is the torque measured inNewton·meters (Nm). The Y-axis 305 of the graph is a measurement of therange of motion in rotation in degrees. The solid (healthy) curve 310 isthe response of a healthy functional spine unit which, for example, caninclude the disc 208 illustrated in FIG. 11. The dotted (degenerate)curve 315 is the response of a diseased or degenerative disc, such asdisc 206 illustrated in FIG. 11. Qualitatively, FIG. 16 indicates thatthe diseased disc rotates more at lower torque than the healthy disc,indicating that there is a greater degree of laxity in the diseaseddisc, which may present as the disc bulging anteriorly and pressingagainst the spinal cord, causing pain, and/or other similar pathology.These measurements can be taken for the spine, as a whole, but, morepreferably, the measurements are made at the vertebrae adjacent to thediseased disc. This is so because the torque-rotation response of theadjacent healthy vertebrae and discs should be the most similar to theresponse of the diseased disc when it was once healthy, a considerationsince it is desired to restore the diseased disc to health.

Referring now to FIG. 17, this graph uses the same axes and scale as thegraph in FIG. 16. In this instance, FIG. 17 plots the solid (momentdifference) curve 320, which is the calculated difference in theresponse between the solid (healthy) curve 310 and the dotted(degenerate) curve 315 in FIG. 16. The dashed (linear) curve 325 is alinear curve fit of the solid (moment difference) curve 320.

A difference and improvement in the embodiments of the spinal implantdisclosed herein is that the geometry of the spinal implant optionallyuses this calculated moment difference as an input in the designprocess. The spinal implant 200 of FIGS. 10 and 11, for example, can bedesigned to have a radius of curvature 121 (illustrated in FIG. 9) thatprovides a desired and known torque response when implanted in thepatient as discussed above. In this example, the spinal implant 200would have a linear torque-rotation response in flexion-extension thathas a slope that is the negative of the dashed (linear) curve 200.

FIG. 18 illustrates the reason for creating a spinal implant thatrelies, in part, on the moment difference between the healthy disc andthe diseased disc. Again, the same axes and scale are used in FIG. 18 asin FIG. 16. In this graph, the original solid (healthy) curve 310 isplotted. Now, however, a spinal implant designed and adjusted for thepatient's pathology, has been implanted as described above with respectto FIGS. 10 and 11. In other words, a spinal implant 200 is nowsupporting the diseased disc 206 and the adjacent vertebrae 204. As canbe seen in FIG. 18, the spinal implant provides a desired stiffness,restoring the response of the dotted (degenerate) curve 315 to that ofthe dashed (linear and degenerate) curve 330 that is similar to thesolid (healthy) curve 210. Qualitatively, it can be seen that with thespinal implant, the rotational response for a given torque is quite nearthat of the healthy disc. While this example is provided for flexion andextension, one having skill in the art would understand that similarmeasurements can be made for lateral extension and axial rotation sothat the results can be used, in part, as an input into the geometry ofthe spinal implant and, therefore, to allow the spinal implant toaccommodate and support the motion of the spine in the three axes asdiscussed above. In brief, embodiments of the spinal implant can bedesigned and adjusted, in part, pre-operatively for an individualpatient's pathology. Embodiments of the spinal implant can restore, atleast in part, a healthy torque-rotation signature to a diseased spine.

A further advantage of the above approach of measuring torque-rotationand similar data for use as an input is that it avoids a problem thatappears in prior art devices. As briefly alluded to, many prior artdevices have a limited range over which they function, typicallyforce-displacement in compression and extension for the devices thatcommonly rely upon springs. These devices are not typically calibratedto an individual. As a result, it is not uncommon for these prior artdevices to use an extension force to distract the diseased disc that istoo large for a given individual, causing undue strain on thesurrounding muscles and ligaments, which may result in undue pain. Insevere cases, the pain this causes might result in the patient undulylimiting his or her range of motion, resulting in nutritionaldeficiencies and other problems associated with minimal or a lack ofmovement in the spine and the disc, which was the outcome to be avoidedinitially.

Embodiments of the spinal implant disclosed herein provide additionalbenefits, such as:

Treating scoliosis, kyphosis, lordosis, and/or similar pathologies: Forexample, with reference to FIG. 4 which illustrates a spine presentingwith scoliosis, embodiments of the disclosed spinal implant can treatthe scoliosis. This is done by using spinal implants that have differenttorque-rotation signatures from each other. That is, rather than usingspinal implants 200 having the same torque-rotation signature asillustrated in FIG. 10, in the instance of scoliosis one of the spinalimplants would have a different and, possibly, opposite, torque-rotationsignature than the other. In addition, a prestressed force may beapplied to one or both of the spinal implants so that they apply a forceto one or both sides of the scoliotic spine. In other words, the torqueand/or any force applied by the spinal implants would be unbalanced inorder to counteract the curvature of the scoliotic spine. For example,in FIG. 4 an extensive force 82 can be applied on the right side of thelumbar area of the spine by one spinal implant, while on the left sideanother spinal implant could apply a compressive force on the left sideof the lumbar area of the spine, tending to cause the lumbar spine tostraighten. Alternatively, or in addition to, the unbalanced forces,torques 84 and 86 could be applied to the spine by the spinal implants.A similar strategy could be used to treat other conditions of the spinethat present similar pathology to scoliosis, such as kyphosis, lordosis,and the like.

Provide distraction of the vertebrae to allow healing of the diseaseddisc: As noted, a spinal implant can be prestressed to provide a torqueand/or extensive force to distract, either anteriorly, posteriorly, orboth, the portion the vertebrae adjacent to a diseased disc. In sodoing, the spinal implants carry or bear a portion of the force normallyborne by the diseased disc, as well as an additional force that staticdevices such as the prior art posterior support 58 in FIG. 5 do notcarry. This arrangement allows sufficient support and space for thediseased disc to heal while still providing for sufficient moment thatstatic prior art devices and procedures (such as spinal fusion) do notprovide. In other words, embodiments of the spinal implant provide anopportunity for the diseased disc to heal, which may allow the spinalimplants to eventually be removed.

Protect spinal cord and periphery nerves: The embodiments disclosedprovide, in part, a measure of protection to the spinal cord andperipheral nerves from being impinged by bulging and/or herniated discsand/or parts of the skeletal structure and other parts of the anatomyafflicted with various pathologies as described above.

Limit range of motion and provide stiffness: The embodiments disclosed,as shown graphically in FIGS. 16-18, restore a measure of stiffness andlimit the range of motion that might otherwise be causing pain, such asthrough muscles overexerting themselves to compensate for the laxitycaused by a diseased disc. By limiting the range of motion, the strainon muscles and ligaments is reduced, thereby reducing risk of injury tothose muscles. Further, laxity is reduced, thereby improving thestructural stiffness (as opposed to the colloquial muscle stiffnesscaused by over-exertion) of the spine.

Kinetics similar to a healthy spine: Related to limiting the range ofmotion discussed above, the motion that embodiments of the spinalimplant provide in the three axes discussed above regarding FIG. 6 issimilar to that of a healthy spine. What this provides is that thepatient's muscles and ligaments do not have to compensate for anunnatural motion of the spinal implant, unlike the case with prior artdevices. In other words, the spinal implant provides more naturalmotion, which would encourage patients to move more with less attendantpain as their muscles would not be compensating or overworking for aprior art spinal implant that does not provide such natural motionaround all three axes. In so doing, the movement provides furthernutrition to the discs, increasing the likelihood that the discs willheal.

Kinematics similar to a healthy spine: Related to the kinetics are thenatural kinematics of embodiments of the spinal implants. As discussedabove, the centers-of-rotation for flexion-extension, lateralextension/bending, and axial rotation, are each located in differentplaces. Prior art devices could not accommodate these separatecenters-of-rotation around more than one axis, if even that, nor couldthey provide for the instantaneous or near instantaneous change in thelocation of the centers-of-motion as a spinal segment moves, nor couldthey provide for motion approximate the motion of a natural helicalaxis. Stated differently, the center-of-rotation of prior art devicesoften was in a different location than the natural center-of-rotation ofthe spine for a given movement. To compensate, patients with prior artdevices suffered strain upon the spinal cord and peripheral nerves,muscle strain caused by the muscles overworking and compensating for thetwo different centers-of-rotation (that of the prior art device and thatof the spine), ligament strain, and, consequently, pain. In contrast,embodiments of the present spinal implant provide centers-of-rotation ineach of the three axes that is the same, or nearly the same, as apatient's natural centers-of-rotation for the spine. Thus, patientstypically have less pain and, consequently, greater movement, to thebenefit of the discs and the spine in general.

Adjust to the individual spine: As noted, embodiments of the spinalimplant can be designed and/or selected preoperatively for an individualpatient's torque-rotation response in order to provide implants thatrestores the diseased disc/spine to near healthy function. Related tothis is the ability to prestress embodiments of the implant prior to, oreven during, surgery to allow the surgeon to further individually tailorthe torque-rotation response of the spinal implant to the individualpatient as determined at the time.

Further, embodiments of the spinal implant are adjustablepost-surgically. As noted, spinal implants made of bioabsorbablematerial will gradually degrade and, in the process, transfer evergreater portions of the force and torque once borne by the spinalimplant back to the patient's spine as it heals. A further benefit ofthis is that these embodiments do not need to be then be surgicallyremoved, reducing cost and risks to the patient. Alternatively,embodiments of the spinal implant can be made from shape-memorymaterials, such as nitinol. The use of shape memory materials allows thespinal implant to be configured in a second geometry or shape uponsurgical implantation and then, upon application of some transformationparameter, such as heat, the spinal implant reverts to a first geometryor shape with different mechanical properties (such as stiffness and/ortorque), thus allow a physician to subsequently alter the treatment ofthe patient without surgical intervention.

Reduced wear: As noted, embodiments of the spinal implant do not havemoving components or components that rub against one another, therebyreducing or eliminating the generation of wear particles. Further,because embodiments of the spinal implant rely upon torsion and/ortorsion beams rather than compression and extension that springs andother similar devices rely upon, reduces or eliminates the risk of thematerial from which the spinal implant is made suffers from fatigueand/or fatigue failure, thereby increasing the reliability of the spinalimplant.

Thus, disclosed above, in addition to the embodiments of the spinalimplant are methods of treating a spine with a spinal implant configuredto provide motion in three axes; methods of treating a spine with aspinal implant that provides kinetics and kinematics similar to that ofa functional spine; methods of treating pathologies that cause the spineto curve; methods of healing a diseased or degenerated disc; methods ofadjusting a spinal implant without surgical intervention; methods ofreducing the wear of a spinal implant; methods of providing a nearhealthy torque-rotation signature to a degenerate spine; and othermethods as will be recognized by one of skill in the art.

As alluded to above, embodiments of the spinal implant are surgicallyimplanted. While the spinal implants disclosed herein can be implantedusing either an anterior, posterior, or lateral incision in the patient,a preferred method is to use a posterior incision. Further, it ispreferred that a minimally invasive procedure be used, such as bylaparoscopy in which only one or a few, small incisions are made and thesurgery is conducted with laparoscopic tools. The methods include makingan incision; providing an embodiment of the spinal implant disclosedherein; using a positioning tool to position the spinal implant andcounter and prestress designed into the spinal implant; and fixing thespinal implant to two adjacent vertebrae. The surgical procedure doesnot require that the disc space be distracted extensively to install thespinal implant, thereby reducing the pain and recovery time endured bythe patient. The method optionally includes implanting spinal implantswith different characteristics, such as different prestressed torques,for treating pathologies such as scoliosis. Fixing the spinal implant tothe vertebrae may be done by applying straps, applying biocompatibleadhesives, installing pedicle screws, and the like, as known in the art.

Alternative methods and positions of placing the spinal implant includelocating them on the anterior side of the spine rather than theposterior side. Spinal implants positioned to the anterior side can bereached through an incision in the patient's back and positioned betweenthe transverse process of adjacent vertebral bodies or mechanicallyattached to the anterior portion of the vertebral body.

The present invention, in various embodiments, includes providingdevices and processes in the absence of items not depicted and/ordescribed herein or in various embodiments hereof, including in theabsence of such items as may have been used in previous devices orprocesses, e.g., for improving performance, achieving ease and/orreducing cost of implementation.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. The foregoing is not intendedto limit the invention to the form or forms disclosed herein. In theforegoing Detailed Description for example, various features of theinvention are grouped together in one or more embodiments for thepurpose of streamlining the disclosure. This method of disclosure is notto be interpreted as reflecting an intention that the claimed inventionrequires more features than are expressly recited in each claim. Rather,as the following claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the followingclaims are hereby incorporated into this Detailed Description, with eachclaim standing on its own as a separate preferred embodiment of theinvention.

Moreover, though the description of the invention has includeddescription of one or more embodiments and certain variations andmodifications, other variations and modifications are within the scopeof the invention, e.g., as may be within the skill and knowledge ofthose in the art, after understanding the present disclosure. It isintended to obtain rights which include alternative embodiments to theextent permitted, including alternate, interchangeable and/or equivalentstructures, functions, ranges or steps to those claimed, whether or notsuch alternate, interchangeable and/or equivalent structures, functions,ranges or steps are disclosed herein, and without intending to publiclydedicate any patentable subject matter.

1. A method of treating a degenerate spinal segment comprising:obtaining a first spinal implant configured to apply a first torque to adegenerate spinal segment having an abnormal curvature and a secondspinal implant configured to apply a second torque to said degeneratespinal segment, each of said spinal implants including: a plurality ofcontiguous segments in which said contiguous segments form an angle at alocation in which two adjacent contiguous segments of the plurality ofcontiguous segments intersect; at least one mounting connectionconfigured to connect said spinal implant to a mounting mechanism, saidmounting mechanism being configured to attach said spinal implant tosaid degenerate spinal segment; and, implanting said first spinalimplant and said second spinal implant to said degenerate spinal segmentso that said first torque and said second torque act to reduce saidabnormal curvature.
 2. The method of claim 1, wherein said first torqueis different from said second torque in at least one of a direction saidtorque is applied and a magnitude of said torque.
 3. The method of claim1, wherein each of said angles are from about 80 degrees to about 110degrees.
 4. The method of claim 1, wherein said implant is made from atleast one of biocompatible plastics, polymers, metals, metal alloys,laminates, shape-memory materials, and bioabsorbable materials.
 5. Themethod of claim 1, wherein said spinal implant includes a radius ofcurvature to provide said torque.